In order to form color photographic images by a subtractive process, a process of forming cyan, magenta and yellow dye images which comprises reducing silver halide grains in exposed or chemically fogged emulsions with a developing agent such as an aromatic primary amine compound, particularly, a N,N-disubstituted p-phenylenediamine compound, to cause reactions of couplers with a simultaneously formed oxidation product of the developing agent is generally utilized.
Couplers used for the above described color developing process are compounds having a phenolic hydroxyl group, an anilinic amino group, an active methylene group or an active methine group which form a dye by oxidative coupling with an aromatic primary amine developing agent.
Suitable couplers which form a cyan dye by reacting with an oxidation product of the color developing agent are phenols and naphthols. Exemplary couplers forming a magenta dye are pyrazolones, pyrazolotriazoles, pyrazolobenzimidazolones, imidazolones, cyanoacetophenones and diaminoaniline, etc. Couplers forming a yellow dye, include .alpha.-amylacetamides, .beta.-ketoacetic acid esters and N,N-malondiamides, etc.
In order to add couplers as described above to photographic emulsion layers, various methods have been proposed. However, it is preferred to use a method of adding couplers which comprises dissolving couplers with a ballast group in the coupler in an organic solvent, and dispersing the solution by emulsification. Characteristics required for such couplers having a ballast group in order to produce color light-sensitive materials having excellent photographic properties are as follows. Namely,
(1) Couplers and developed dyes formed by color development have high solubility in high boiling point organic solvents (for example, tricresyl phosphate) used for dispersing the couplers.
(2) Silver halide photographic emulsions having dispersed therein the couplers have high stability and when the emulsions are applied to a support and dried, stable coating films are obtained.
(3) They have an excellent antidiffusion property and do not diffuse into other layers.
(4) They have an excellent dyeing property, and dyed color images have an excellent spectral absorption characteristic. Further, they have good color and density stabilities and high fastness to light.
(5) They can be obtained in good purity and high yield from inexpensive raw materials by a simple synthetic process.
Hitherto, many attempts of modifying the structure of ballast group have been made in order to improve the above described characteristics. Examples of these attempts have been described in Japanese Patent Publication Nos. 5582/67, 5391/71 and 27563/64, U.S. Pat. Nos. 2,589,004 and 2,909,573, Japanese Patent Publication No. 3660/69, U.S. Pat. Nos. 2,474,293, 2,039,970 and 2,920,961, Japanese Patent Publication No. 36078/71, U.S. Pat. No. 2,589,004, British Pat. No. 994,838, Japanese Patent Publication No. 19026/71, U.S. Pat. No. 2,659,329, British Pat. No. 1,813,832, Japanese Patent Application (OPI) No. 76834/78, Japanese Patent Publication No. 36856/79, Japanese Patent Application (OPI) No. 82411/78, German Patent Application (OLS) No. 2,707,488, and Japanese Patent Application (OPI) Nos. 139534/78, 141622/78, 23528/79, 48541/79, 65035/79, 99433/79 and 121126/79, etc.
However, couplers having a ballast group known hitherto have some disadvantages and they do not satisfy the above described characteristics which are required for them. Many of these couplers with an oleophilic ballast group have excellent stability and antidiffusibility in emulsion layers, spectral absorption characteristics of color images, durability of color images and aptitude for synthesis as compared with other types of coupler (for example, couplers having an acid group which are added to emulsion layers as a micellar aqueous solution). However, those which have a satisfactory color forming property have not be found, yet. In rapid processing at high temperature which has been used actively in recent years, the color forming property is particularly important, and insufficient color formation becomes a serious problem. In order to compensate for this insufficient color formation, depending on the circumstances addition of an organic solvent such as benzyl alcohol as a color forming accelerator to the developing solution has been employed. However, organic solvents for accelerating color formation have some disadvantages. For example,
(1) Since they are absorbed in the emulsion layers in the development step, the amount thereof in the developing solution is reduced with deterioration of color formation occurring.
(2) They are carried into the bleaching solution or the blixing solution with obstruction of desilvering or deterioration of dye densities occurring.
(3) They remain in the light-sensitive materials after processing deteriorating the fastness of color images.
(4) They are admixed with waste liquors causing an increase of B.O.D. and C.O.D. in the waste liquors. Therefore, it has been highly desired to remove or reduce the amount of organic solvents for accelerating color formation.
In couplers containing a ballast group having a p-hydroxyphenylenesulfonyl group or a p-hydroxyphenylenesulfinyl group at the terminal of the group as described in European Patent Publication (Unexamined) No. 73636, improvement of the color forming property is observed as compared with prior couplers, but even so the degree of improvement is not sufficient, yet. Further, they have the disadvantage of having low solubility in organic solvents for dispersing couplers.